Method for large-scale fabrication of atomic-scale structures on material surfaces using surface vacancies

ABSTRACT

A method for forming atomic-scale structures on a surface of a substrate on a large-scale includes creating a predetermined amount of surface vacancies on the surface of the substrate by removing an amount of atoms on the surface of the material corresponding to the predetermined amount of the surface vacancies. Once the surface vacancies have been created, atoms of a desired structure material are deposited on the surface of the substrate to enable the surface vacancies and the atoms of the structure material to interact. The interaction causes the atoms of the structure material to form the atomic-scale structures.

FIELD OF INVENTION

[0001] The present invention generally relates to processes foratomic-scale modification of surfaces, and more particularly to methodsfor fabricating atomic-scale structures on a surface of a material on alarge-scale with atomic precision.

BACKGROUND

[0002] Atomic-scale modification of material surfaces has beendemonstrated since the late 1980's with the advent of the scanningtunneling microscope (STM). Initially, the STM had been used to obtainatomic-resolution images of surfaces, but later, the STM has also beenused for atomic-scale modification of surfaces. The STM includes aconducting needle which is held close to a conducting surface. Byadjusting the position and the voltage applied to the tip of the needle,individual or cluster of atoms are removed from the surface anddeposited on the STM tip. The tip is then moved to a predeterminedsurface site and the atoms are redeposited.

[0003] Over the years various techniques, including direct manipulationof atoms through UHV (ultrahigh vacuum)-STM tips, nano-patterning bychanging local chemical-state of surfaces, etc., have been proposed toachieve device miniaturization. These known techniques, however, havenot been utilized for industrial applications. This is primarily due tothe fact that these techniques can only modify very localized area(generally tens of nanometers). The STM-based technique is also anextremely slow process, which requires one-by-one positioning of eachindividual or clusters of atoms. The traveling speed of the STM tip istypically about 0.4 nm/s, therefore it would require enormous amount oftime (months) to scan just one piece of an 8-inch Si wafer. These knownSTM-based techniques may be useful for scientific studies on growth ofatomic-scale structures at a small-scale. However, they are notappropriate as a large-scale manufacturing technique for the use in thesemiconductor industry.

SUMMARY OF THE INVENTION

[0004] The present invention relates to a method for formingatomic-scale structures on a surface of a substrate on a large-scale.The method includes creating a predetermined amount of surface vacancieson the surface of the substrate by removing an amount of atoms on thesurface of the material corresponding to the predetermined amount ofsurface vacancies. Once the surface vacancies have been created, atomsof a desired structure material are deposited on the surface of thesubstrate to enable the surface vacancies and the atoms of the structurematerial to interact. This interaction causes the atoms of the structurematerial to form the atomic-scale structures.

DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 is a sectional view of a substrate material prior to theformation of surface vacancies in accordance with embodiments of thepresent invention;

[0006]FIG. 2 is a sectional view of the substrate material of FIG. 1,showing surface vacancies formed in accordance with embodiments of thepresent invention;

[0007]FIGS. 3 and 4 are sectional views of a substrate materialillustrating a method for controlling the amount of surface vacanciesthat are formed on different areas on the surface of the substratematerial;

[0008]FIG. 5 is a sectional view of the substrate material withatomic-scale structures formed on the surface, generally showing amethod for forming atomic-scale structures on the surface of thesubstrate material in accordance with an embodiment of the presentinvention; and,

[0009]FIG. 6 is a plan view of the substrate material with atomic-scalestructures of FIG. 5, generally showing the atomic-scale structuresformed on the surface of the substrate material.

DETAILED DESCRIPTION OF THE INVENTION

[0010] Turning to FIGS. 1-2, a method of fabricating atomic-scalestructures on a material surface in accordance with embodiments of thepresent invention is described. In FIG. 1, a section of a materialsubstrate 10, a Si substrate, for example, is shown in <110> zone axis(a sectional view), and has layers of Si atoms 12 including a firstmonolayer 14 and a second monolayer 16 extending along the surface 18 or<110> zone axis of the substrate 10. In accordance with one embodimentof the present invention, the surface 18 undergoes a reactive plasmaetching process, preferably using predetermined partial pressure O₂sufficient to remove atoms 12 from the surface 18 of the substrate 18,and create surface vacancies 19 at the locations evacuated by surfaceatoms 12 (best shown in FIG. 2). Other gases such as Cl₂, F₂, HF, CFCl₃,CF₂Cl₂, CCl₄, BCl₃/Cl₂, CF₄/O₂, SF₆, and NF₃, for example, are alsosuitable for the plasma etching process.

[0011] Using higher partial pressure of gas results in more surfaceatoms 12 from being removed from the surface 18, thereby creatingcorresponding number of surface vacancies 19. Lower partial pressure gashas the opposite effect. Accordingly, partial pressure can be rangingfrom tens of mT(10⁻³ Torr) to 10⁻¹⁰ Torr. For example, experiments haveshown that in a Si substrate 10 having approximately 3% surfacevacancies per square centimeter (1.017×10¹³ dimers vacancies per cm⁻²)before the O₂ etching process, the percentage of surface vacanciesincreased to 15% (5.085×10¹³ dimers vacancies per cm⁻²) at O₂ exposureof 2.5L (where 1L=1.33×10⁻⁶ Torr×1 s), and to 30% (1.017×10¹⁴ dimersvacancies per cm⁻²) at O₂ exposure of 10.0L. It should be noted thatthese results were obtained with the substrate temperature at 700° C.

[0012] Turning now to FIGS. 3 and 4, conventional lithography andisolation techniques (e.g. LOCOS or STI) may be employed to define orpattern areas that require different orientation and distribution ofatomic-scale structures, (if desired and/or necessary), in conjunctionwith reactive plasma etching process. In FIG. 3, for example, only anarea 20 of the surface 18 is subjected to a low partial pressure O₂etching gas, while adjacent areas 22, 24 are protected or masked fromthe O₂ etching gas by a photoresist. As a result, a number of the Siatoms 12 in only this area 20 are removed from the surface 18.

[0013] Turning to FIG. 4, the area 20 etched with low partial pressureO₂ gas is now masked from the O₂ etching gas, and adjacent areas 22, 24are exposed to a higher partial pressure O₂ etching gas than in the area20. As a result, the areas 22, 24 that are exposed to the higher partialpressure O₂ etching gas have a higher percentage of surface vacanciesthan the area 20 exposed to the lower partial pressure gas.

[0014] Turning now to FIGS. 5 and 6, after the surface 18 has beenetched, as shown in FIGS. 2 or 4, blanket deposition of atoms 26 ofdesired material, such as Er atoms, for example, is carried outsimultaneously on surface 18 at predetermined temperatures, to formatomic-scale structures 28 on the entire surface. In experiments inwhich Er atoms were deposited on a Si substrate 10, for example, thedeposition was performed at a substrate's temperatures of approximately700° C. It should be understood, however, that the substrate'stemperature required can vary significantly from about room temperatureto upwards of approximately 1,500° C., depending on the type ofsubstrate and atomic-scale structures to be formed. For example, thetemperature required for forming W atomic-scale structures on the Sisubstrate 10 would be much higher than the temperature required to formEr atomic-scale structures.

[0015] The deposited atoms 26 react with the surface vacancies 19created. The interaction and bonding relationship between the depositedmaterials and substrate results in the formation of atomic-scalestructures in a self-assembly manner. The distribution and orientationof these atomic-scale structures 28 on a specific area generallycorrespond to those of the surface vacancies 19.

[0016] Experimental results show that specific bonding relationship isestablished during the formation of atomic-scale structures. Thisbonding relationship varies from materials to materials and can becontrolled by the amount of surface vacancies. For example, in the caseof Er atoms deposited on Si(001) substrate with ˜25% of surfacevacancies. Rearrangement of surface vacancies occurs upon annealing at700C. and its interaction with Er atoms results in the formation ofregular array of Er atomic-scale structures. With this specificcondition, the Er atomic-scale structures are formed on top of thevacancies sites with six Si atoms surrounding them. A minimum spacing of1.086 nm is measured between the atomic-scale structures along [100]direction.

[0017] In accordance with another embodiment of the present invention,the surface vacancies 19 on the surface 18 of the substrate 10 (bestshown in FIG. 2) are created through high temperature annealing in avacuum chamber (not shown). In this embodiment, the substrate 10 isplaced in a vacuum chamber at predetermined pressure and temperature fora predetermined time period. In experiments using Si substrate 10, forexample, the desired amount of surface vacancies 19 were created atabout 1,100° C. and at a pressure of 5×10⁻¹⁰ Torr for 180 second. Itshould understood, however, that the parameters for creating specificamount of surface vacancies can vary widely depending on the choice ofsubstrate material. The pressure can range anywhere from about 10⁻³ T toabout 10⁻¹⁰ T, the temperature can be anywhere from room temperature to1,500° C., and the length of time from few seconds to hours.

[0018] It should be understood that other methods can be employed tocreate surface vacancies 19 on the material surface 18 in addition tothe two described above, ion-sputtering, for example. Also, while thepresent invention has been described using Er as an example for formingthe atomic-scale structures 28 on a Si substrate 10, it should beunderstood that the methods described above is applicable to many othersuitable combinations of materials. Some examples of materials for useas the substrate 10 include SiGe, SiC, Ge, GaAs, GaAlAs, GaAlAsP, etc.,and the atomic-scale structures 28 can be formed from almost any knownelements and compounds including rare-earth metal (e.g. Gd, Er, Dy, Ybetc.), Group IV elements (e.g. C, Ge, Si, Sn etc.), transition metals(e.g. Co, Ni, Ti, Cu etc.) and many other organic materials. Theparameters specified above for creating and controlling the amount ofsurface vacancies 19 and for depositing atoms for forming atomic-scalestructures 28 on the substrate surface 18 may be changed accordingly fordifferent materials systems.

[0019] In accordance with another embodiment of the present invention,at least one additional layers of atomic-scale structures of differentmaterials can be formed on top of the previously formed layer ofatomic-scale structures 28. This is accomplished by treating theprevious layer of the atomic-scale structure 28 as a substrate andforming the additional layer on the surface of the previously formedatomic-scale structure 28 in the same manner described above for formingthe previously formed atomic-scale structure 28.

[0020] From the foregoing description, it should be understood that animproved method for forming atomic-scale structures on a surfacematerial on a large-scale has been shown and described which has manydesirable attributes and advantages. Predetermined amount of surfacevacancies are created on the surface of the material and atoms ofdesired materials are deposited on the modified surface to form theatomic-scale structures.

[0021] While various embodiments of the present invention have beenshown and described, it should be understood that other modifications,substitutions and alternatives are apparent to one of ordinary skill inthe art. Such modifications, substitutions and alternatives can be madewithout departing from the spirit and scope of the invention, whichshould be determined from the appended claims.

[0022] Various features of the invention are set forth in the appendedclaims.

What is claimed is:
 1. A method for forming atomic-scale structures on asurface of a substrate on a large-scale, said method comprising thesteps of: creating a predetermined amount of surface vacancies on thesurface of the substrate by removing an amount of atoms on the surfaceof the substrate corresponding to said predetermined amount of surfacevacancies; and, depositing atoms of a desired structure material on thesurface of the substrate to enable said surface vacancies and said atomsof said structure material to interact, said interaction causing saidatoms of said structure material to form the atomic-scale structures. 2.The method as defined in claim 1 wherein said surface vacancies arecreated by a reactive gas etching process.
 3. The method as defined inclaim 2 wherein any one of O₂, Cl₂, F₂, HF, CFCl₃, CF₂Cl₂, CCl₄,BCl₃/Cl₂, CF₄/O₂, SF₆, and NF₃ gas is used in said reactive gas etchingprocess.
 4. The method as defined in claim 1 wherein said surfacevacancies are created in a vacuum chamber by a high temperatureannealing process.
 5. The method as defined in claim 1 wherein saidsurface vacancies are created by an ion sputtering process.
 6. Themethod as defined in claim 1 wherein said atoms of said structurematerial are deposited on the substrate through a blanket depositionprocess.
 7. A method for forming atomic-scale structures on a surface ofa substrate on a large scale, said method comprising the steps of:creating a first predetermined amount of surface vacancies on a firstselect area on the surface of the substrate by removing an amount ofatoms on said first select area corresponding to said firstpredetermined amount; creating a second predetermined amount of surfacevacancies on at least one other select area on the surface of thesubstrate by removing a second amount of atoms on said at least oneother select area of the surface of the substrate corresponding to saidsecond predetermined amount; and, depositing atoms of a desiredstructure material on the surface of the substrate to enable saidsurface vacancies on said first select area and said at least one otherselect area, and said atoms of said structure material to interact, saidinteraction causing said atoms of said structure material to form theatomic-scale structures.
 8. The method as defined in claim 7 whereinsaid surface vacancies in said first select area and said at least oneother select area are created by a reactive gas etching process.
 9. Themethod as defined in claim 8 further including the steps of blockingexposure of said at least one other select area to said reactive gasetching process when said surface vacancies are being created in saidfirst select area, and said first select area to said reactive gasetching process when said surface vacancies are being created in said atleast one other select area.
 10. The method as defined in claim 8wherein any one of O₂, Cl₂, F₂, HF, CFCl₃, CF₂Cl₂, CCl₄, BCl₃/Cl₂,CF₄/O₂, SF₆, and NF₃ gas is used in said reactive gas etching process.11. A method for forming atomic-scale structures on a semiconductorsubstrate on a large scale, said method comprising the steps of:creating a predetermined amount of surface vacancies on a surface of thesemiconductor substrate by removing an amount of atoms on said surfaceof the substrate corresponding to said predetermined amount of saidsurface vacancies; and, depositing atoms of a desired structure materialon the surface of the substrate to enable said surface vacancies andsaid atoms of said structure material to interact, interaction causingsaid atoms of said structure material to form the atomic-scalestructures.
 12. The method as defined in claim 11 wherein saidsemiconductor substrate is any one of Si, SiGe, SiC, Ge, GaAs, GaP,AlAs, AlP, GaAlAs, GaAlAsP and any other combination of Group III, IV, Velements.
 13. The method as defined in claim 11 wherein said surfacevacancies are created by a reactive gas etching process.
 14. The methodas defined in claim 13 wherein any one of O₂, Cl₂, F₂, HF, CFCl₃,CF₂Cl₂, CCl₄, BCl₃/Cl₂, CF₄/O₂, SF₆, and NF₃ gas is used in saidreactive gas etching process.
 15. The method as defined in claim 11wherein said surface vacancies are created in a vacuum chamber by a hightemperature annealing process.
 16. The method as defined in claim 11wherein said surface vacancies are created by an ion sputtering process.17. The method as defined in claim 1 wherein said atoms of saidstructure material are deposited on the surface of the substrate througha blanket deposition process.
 18. A method for forming a plurality oflayers of atomic-scale structures on a surface of a substrate on alarge-scale, said method comprising the steps of: creating apredetermined amount of first surface vacancies on the surface of thesubstrate by removing an amount of atoms on the surface of the substratecorresponding to said predetermined amount of first surface vacancies;depositing atoms of a first desired structure material on the surface ofthe substrate to enable said first surface vacancies and said atoms ofsaid first structure material to interact, said interaction causing saidatoms of said first structure material to form a first layer of theatomic-scale structures; creating a predetermined amount of secondsurface vacancies on a surface of said first layer by removing an amountof atoms on the surface of said first layer corresponding to saidpredetermined amount of second surface vacancies; and, depositing atomsof a second desired structure material on said surface of said firstlayer to enable said second surface vacancies and said atoms of saidsecond structure material to interact, said interaction causing saidatoms of said second structure material to form a second layer of theatomic-scale structures.